The invention relates to a rope deflection and a synthetic fiber rope suitable for use with it.
Especially in materials handling technology, as for example on elevators, in crane construction, in mining, or similar applications, ropes are an important element of machinery and subject to heavy use. As a loaded rope passes over a deflection element, as for example a rope pulley, rope sheave, or rope drum, etc. it is bent over the deflection element, which causes special movements of the strands of the rope.
A correspondingly used rope is known, for example, from the European patent document EP 0 672 781 A1. In respect of service life, high wear resistance, and high reverse bending strength, the multi-layered parallel twisted aramide fiber stranded rope provides very satisfactory values; however, it has been established that when the permanently loaded synthetic fiber rope is deflected on a traction sheave, a rope drum, a rope pulley, or similar, within a short period of operation corkscrew-like rope deformations can form in the tensioned area of the covering layer of strands, which could lead to a reduction in the breaking force of the rope or even to failure of the rope.
The present invention concerns a permanently reliable rope deflection with a synthetic fiber rope passing over pulleys or traction sheaves.
According to the invention this objective is achieved by means of a rope deflection wherein the synthetic fiber rope lies on the deflecting element at least along a length of three lay lengths of the rope lay.
The essence of the invention is therefore that the diameter of the deflection element and the lay length of the synthetic fiber rope are adapted to each other in such a way that within the angle of wrap the strands of the covering layer of strands always lie on the deflection element at least three times.
Extensive tests have shown that the smaller the arc of wrap and the larger the lay length of the covering layer of strands, the more strands are displaced as bending takes place over a rope pulley, a rope sheave, a rope drum, or similar. The shorter the lay length and the larger the deflecting element, the smaller are the movements of the strands relative to each other.
From this the knowledge has been gained that the shorter the rope lay length of the covering layer, the smaller the diameter of the rope pulley, traction sheave, or similar that can be selected. In addition, according to the present invention it has been established as a minimal requirement that within the angle of wrap the strands should lie on the traction sheave at least three times for an irreversible displacement of strands to be reliably avoided.
Moreover, in developing the invention further, it became known that the less frequently the moving strand lies on the base of the groove of the driven rope sheave, the more easily overlengths can occur in the area experiencing tension.
It is well known that the function of such rope drives is based on the driving force being transferred to the rope via the section of rope which is in contact with the traction sheave at any specific time. As the rope passes over the traction sheave it is bent and, as this occurs, especially in the area in the covering layer of strands which is experiencing tension, the missing length is correspondingly displaced. At the same time, mainly in the area of the rope experiencing pressure, the strands are pushed away from the traction sheave. To meet these many and varied stresses on the rope, the internal balancing of the rope system is of especial importance.
For this reason, according to a preferred embodiment of the invention, in the case of a rope drive with a synthetic fiber rope with intersheath, the formation of overlengths in the area of tension is prevented if the diameter of the traction sheave and the length of the rope lay are adapted to each other in such a way that the strands of the covering layer of strands lie on the traction sheave at least four times. With this form of rope with intersheath, overlengths in the area of tension are less reversible the higher the coefficient of friction between the intersheath and the covering layers of strands, because when the rope is loaded the strands are fixed by the constrictive pressure.